I'm aware of the armour thickness,I took a long look at about 10-20 tanks' descriptions and learned their weaknesses,but it happenes most of the times:

After I take a shot at one spot and it doesn't penetrate/inflict a critical hit I fire at anoter weak spot,like the thread wheels/the gap between the turret and the tank body.Still bounces off.There are 2-3 tanks,which names I don't remember that are ******* invincible!There was this medium russian tank that had this ******* diamond
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and 4 teammates fired upon it from everywhere and from about 60 shots only 3-4 penetrated...

They've done great,the game is epic,but no..they still need another update on their physics.

Part of that is because shots don't always go straight, which they are fixing with the 8.6 update. Part of it is that treads act as spaced armor, and they don't have damage hitboxes, so you'll never do any serious damage.

It sounds like you're up to tier 5 tanks, so I can say that most lower-tier guns have pitiful penetration and you won't be able to penetrate most tanks without aiming for weak spots (and actually hitting them). Some, like the KV-1 and AT 2, you simply may not be able to penetrate - leave those guys to the big guns, HE guns, and SPGs (artillery).

The KV-1 has two glaring weak spots (or rather, spots that you can reliably penetrate) from the front, on the front glacis plate (on the tank body). It's the two vertical portions, separated by a steeply sloped portion, so aim for the top or bottom plate. For more info, check out the weak spot guide:
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i play this game with my friend from time to time, my fondest memory is when he and i were both artillery and someone tried to sneak up on us. I turned around and shot blindly at him and took him out in one shot. Twas a glorious day.